1. Field of the Invention
The present invention relates to a sequential monitoring method and apparatus for monitoring the working state of a production line.
2. Prior Art
Automated production facilities usually include production lines along which products or partially-fabricated products to be processed are transported by belt conveyors or the like and on which products various work operations are performed according to predetermined sequences. If an abnormal condition of transporting or work operation occurs on a production line, the operation of the line is quickly stopped to avoid escalation into more serious trouble.
For monitoring the working state of a production line, detectors such as microswitches are provided along the production line and the electrical outputs of the detectors are fed to a sequence diagnostic apparatus as disclosed in, for example, Japanese Patent Kokai No. 59-62912. The sequence diagnostic apparatus evaluates the state of the production line based on the timing of the outputs of the detectors and generates triggering signals such as an emergency signal upon detecting an abnormal state. On the production line, if the triggering signals are output to stop the operation of the production line, the apparatus reads out the data stored in the memories, for making an analysis of the cause of the abnormal state. The data on the progress of the work is printed out on data sheets in a predetermined format.
In the conventional sequence monitoring method, as reference data used for judgment of an abnormal state are previously input in the sequence diagnostic apparatus, the work involved in inputting the data and calculating from the reference data is burdensome. Furthermore, when the material, kind, or size of the products or partially fabricated products to be processed is changed, the sequence of the product line accordingly changes and new data should be input into the sequence diagnostic apparatus, which limits its practical uses. Since the triggering signals are output only in the case of an abnormal state of the production line, which line must then be stopped, the stage at which the line gradually assumes an abnormal state cannot be detected. That is, the conventional method and its system cannot prevent abnormal states. Still further, since the sequence diagnostic apparatus outputs all of the data, it takes a longer time to analyze the data on the abnormal state, and especially to identify the work as to which the problem arose.